"William Morse"  wrote in message
news:brcqki$7pd$1{at}darwin.ediacara.org...
> Brett Aubrey  wrote in
> news:batirr$qfe$1{at}darwin.ediacara.org:
>
> > "r norman"  wrote...
> >> On Sat, 24 May 2003 17:24:44 +0000 (UTC), Brett Aubrey
> >>  wrote:
> >> > wrote:
> >> >> I contend that due to my model, no species 'evolves'
> >> >> unless they are forced to adapt to harsh changes -
thus
> >> >> As environmental adaptation increases:
> >> >>    directional and diversifying selection decreases
> >> >>    AND stabilizing selection increases.
> >> >>     (and vice versa)
> >> >> So I contend that the brain development in hominids
> >> >> was due to the harsh environmental weather at the
time:
> >> >> 
> >> >By way of example, I might point to (my understanding
of) the
> >> >giraffe's neck, tongue, etc. to permit better access
to fairly
> >> >poorly exploited Acacia trees;    
> >> Be careful of the examples you use for evolution!
There is evidence
> >> that the giraffe's neck is NOT an adaptation for
feeding high
> >> above the ground, but rather is the result of sexual
selection.  See
> >>   R.E. Simmons and L. Scheepers,
> >>   "Winning by a Neck: Sexual Selection in the
> >>     Evolution of the Giraffe"
> >>   American Naturalist 148:771-786 (1996)
> >
> > Thanks muchly for this, "r norman" - I'll certainly
remember it in the
> > future.  After perusing the Web for a while, I see this
area is widely
> > misunderstood as well as being somewhat controversial.
Your statement
> > starts with "There is evidence that... " and many of the
sources I
> > looked at varied significantly, so I still have one
question:
> > Is there any support for the high, unexploited tree
"reason" among the
> > professionals (biologists and such), or is sexual
selection really the
> > only main reason cited these days (i.e. there could be
more than one
> > underlying reason, at least in theory).
>
>
> Certainly there could be more than one reason. The sexual
selection
> theory is interesting and supported by some behavioral
evidence, but it
> is also possible that the long neck was first selected for
by feeding
> high above the ground and then became involved in sexual
competition.
> Long necks have appeared many times in evolution - perhaps
because they
> can be created by a relatively simple change in
developmental genes. But
> the reason may also be that they provide access to a
modified food niche
> while maintaining most of the rest of a suite of
adaptations to an
> existing ecosystem. If you want to eat leaves high up on
trees, you might
> be better off in becoming a small animal adept at
climbing. If you are
> already a large grazer with hoofs, there is no way to get
there from
> here. Growing a long neck is an available option - but it
may still take
> the spur from sexual selection to drive a bunch of happy
low tree grazers
> into developing the enhanced cardiovascular pumping system
that allows
> giraffes to browze the treetops without fainting.

For a while I've been wondering if we've given up Lamarckism
too quickly--in this sense:

We know that brain development of infants (as well as the
whole body in fact) depends on the release of certain
biochemicals at specific times in life dictated by our
evolved genetic programs... what if evolution works on
selecting for those genes associated with the release of
greater quantities of biochemicals which are responsible for
a beneficial physical result, e.g., neck lengthening (would
growth hormone of something related work here?) Maybe
stretching giraffe necks actually _can_ affect the genes in
this way--Is it possible for hormone releases to be mediated
in this way, and provide some linkage to genotype? Anyone up
for a neo-Lamarckian movement?  :-))        ...tonyC

>
> Yours,
>
> Bill Morse
>
---
þ RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info{at}bbsworld.com

---
 * RIMEGate(tm)V10.2áÿ* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 12/14/03 11:36:37 AM